This section describes the core research projects, which include both developing the technology required for high-resolution x-ray imaging of biological specimens and the preparation of those specimens. Our primary focus in the initial phase of the proposed program is the construction of a soft x-ray, zone plate microscope. In section D.1.a, we provide a detailed discussion of the construction of each of the basic components of the x-ray microscope. In section D.1.b, we describe development of the technologies required to image biological specimens. D.1.b.i outlines requirements for high throughput, tube cryo-tomography of samples that grow in suspension, such as yeast or hemopoietic cells. Since the axially symmetric cylindrical sample can undergo complete 360-degree rotation, only single-axis rotation is required for complete tomography. In D.1.b.ii we also discuss the specimen stage required for flat sample cryo tomography and imaging. This stage is suitable for imaging flat samples, such as tissue culture cells, or thick tissue cryosections. Sample substrates can be any kind of thin membrane, such as silicon or silicon nitride windows, or conventional substrates used for TEM. Due to the limits on tilt angle imposed by the microscope geometry of (75 degrees, dual axis tilt capability will be required for the most complete tomographic data acquisition and reconstruction. The success of any high-resolution cryogenic imaging technique requires that the sample be rapidly frozen and transferred to the cryo-imaging stage. For this task we will adapt techniques used for cryo TEM to fit the needs of the x-ray microscope. Each of the developments described below builds upon our existing prototype technology, but all of them involve significant improvements and new developments to optimize the performance and usability of the microscope. Core Research Project 1: Transmission Soft X-ray Microscope (Mark Le Gros, Erik Anderson, Carolyn Larabell) (Subscore: 128) Description (provided by applicant) The goal of this core research project is to construct a full field, soft x-ray transmission microscope optimally designed for imaging biological specimens and for cryo-tomography of both cylindrical and fiat specimens. Summary of Panel Discussion The committee believes that this is the strongest component of the proposal. The existing XM-1 microscope, which is the prototype of XM-2, is clearly an excellent instrument, and to copy it will give a quite workable system. The proof-of-principle produced already by Dr. Larabell's group for biological imaging, the extremely fine reputation of the Center for X-ray Optics (CXRO) for construction of beamlines, and the very strong support offered by the Science Advisory Committee and administration of the Advanced Light Source (ALS) all support this view that the microscope can be constructed and will meet it's design goals. The ideas expressed at the site visit for enhancements of the microscope - correlated scanning of the condenser zone plate and pinhole, automated objective ZP selection, and automated alignment - are innovative and will make XM-2 a superior instrument.